Content-based networking is an emerging technology; because of its youth, little thought has been given to its security. Content-based networking achieves efficiency via reuse, i.e., multiple nodes requesting the same content, whereas most security mechanisms work by restricting access based on possession of some secret. There is a fundamental tension between reuse and restriction, making it non-trivial to design a security solution for content-based networks without compromising efficiency. Further, since content-based networking uses content descriptions (e.g., metadata) rather than node identifiers as the way to move data around a network, traditional encryption and access control techniques are difficult to apply.